Bisphosphonates inhibit prostate and breast carcinoma cell adhesion to unmineralized and mineralized bone extracellular matrices.

The molecular mechanisms by which tumor cells induce osteolytic metastases are likely to involve tumor cell adhesion to bone as well as the release of soluble mediators from tumor cells that stimulate osteoclast-mediated bone resorption. Bisphosphonates (BPs) are powerful inhibitors of the osteoclast activity and are, therefore, used in the treatment of cancer-associated osteolytic metastases. Here, we investigated the effect of BPs on breast and prostate carcinoma cell adhesion to unmineralized and mineralized bone extracellular matrices. BP pretreatment of tumor cells inhibited tumor cell adhesion to unmineralized and mineralized osteoblastic extracellular matrices in a dose-dependent manner. In contrast, BP did not affect adhesion of normal cells (fibroblasts) to extracellular matrices. The order of potency for four BPs in inhibiting tumor cell adhesion to extracellular matrices was found to be: ibandronate > NE-10244 (antiresorptive active pyridinium analogue of risedronate) > pamidronate > clodronate. BP did not affect [3H]thymidine incorporation by tumor cells, as assessed by a mitogenesis assay, indicating that BP did not exert any cytotoxic effect at concentrations used to inhibit tumor cell adhesion. NE-58051, the inactive pyridylpropylidene analogue of risedronate, had no inhibitory effect on tumor cell adhesion compared to that observed with its active counterpart NE-10244, suggesting that the mechanism of action of BP on tumor cells involved a stereospecific recognition step. Although integrins mediate cell-matrix interactions, BP recognition by tumor cells did not modulate cell surface integrin expression. In conclusion, our results provide evidence for a direct cellular effect of BP in preventing tumor cell adhesion to bone, suggesting that BPs may be useful agents for the prophylactic treatment of patients with cancer that is known to preferentially metastasize to bone.

Bisphosphonates inhibit breast and prostate carcinoma cell invasion, an early event in the formation of bone metastases.

The molecular mechanisms by which tumor cells metastasize to bone are likely to involve invasion, cell adhesion to bone, and the release of soluble mediators from tumor cells that stimulate osteoclast-mediated bone resorption. Bisphosphonates (BPs) are powerful inhibitors of the osteoclast activity and are, therefore, used in the treatment of patients with osteolytic metastases. However, an added beneficial effect of BPs may be direct antitumor activity. We previously reported that BPs inhibit breast and prostate carcinoma cell adhesion to bone (Boissier et al., Cancer Res., 57: 3890-3894, 1997). Here, we provided evidence that BP pretreatment of breast and prostate carcinoma cells inhibited tumor cell invasion in a dose-dependent manner. The order of potency for four BPs in inhibiting tumor cell invasion was: zoledronate > ibandronate > NE-10244 (active pyridinium analogue of risedronate) > clodronate. In addition, NE-58051 (the inactive pyridylpropylidene analogue of risedronate) had no inhibitory effect, whereas NE-10790 (a phosphonocarboxylate analogue of risedronate in which one of the phosphonate groups is substituted by a carboxyl group) inhibited tumor cell invasion to an extent similar to that observed with NE-10244, indicating that the inhibitory activity of BPs on tumor cells involved the R2 chain of the molecule. BPs did not induce apoptosis in tumor cells, nor did they inhibit tumor cell migration at concentrations that did inhibit tumor cell invasion. However, although BPs did not interfere with the production of matrix metalloproteinases (MMPs) by tumor cells, they inhibited their proteolytic activity. The inhibitory effect of BPs on MMP activity was completely reversed in the presence of an excess of zinc. In addition, NE-10790 did not inhibit MMP activity, suggesting that phosphonate groups of BPs are responsible for the chelation of zinc and the subsequent inhibition of MMP activity. In conclusion, our results provide evidence for a direct cellular effect of BPs in preventing tumor cell invasion and an inhibitory effect of BPs on the proteolytic activity of MMPs through zinc chelation. These results suggest, therefore, that BPs may be useful agents for the prophylactic treatment of patients with cancers that are known to preferentially metastasize to bone.

Additive antitumor activities of taxoids in combination with the bisphosphonate ibandronate against invasion and adhesion of human breast carcinoma cells to bone.

A very common metastatic site for breast carcinoma is bone. Metastatic breast carcinoma cells stimulate osteoclast-mediated bone resorption leading to osteolysis. Bisphosphonates are powerful inhibitors of osteoclast activity, and are therefore used in combination with standard chemotherapy or hormonal therapy for the treatment of cancer-associated osteolytic metastases. However, there may be an added beneficial effect of the bisphosphonates, that is, additive or synergistic activities with cytotoxic agents. Here, we investigated the effects of the bisphosphonate ibandronate in combination with taxoids (taxol and taxotere) on induction of apoptosis, invasion and adhesion of breast carcinoma cells to bone. Ibandronate did not induce apoptosis of human MDA-MB-231 breast carcinoma cells, nor did it enhance the effectiveness of taxoid-induced apoptosis in MDA-MB-231 cells. In contrast, ibandronate enhanced the antitumor activity of taxoids against invasion and cell adhesion to bone. Our findings raise the interesting possibility that the combination of bisphosphonates and taxoids may be useful for the treatment of patients with cancer types that are known to metastasize preferentially to bone.

[Thrombospondins, tumor angiogenesis and breast cancer]. / Thrombospondines, angiogenèse tumorale et cancer du sein.

Thrombospondin-1 and -2 are extracellular matrix proteins that are overexpressed in breast cancer tissue. Their role in breast cancer remains unknown. This article reviews the potential effects of thrombospondin-1 and -2 in breast cancer tumori genesis and metastatic dissemination.

CD36 mediates binding of soluble thrombospondin-1 but not cell adhesion and haptotaxis on immobilized thrombospondin-1.

In this study, we examined the binding of soluble TSP1 (and ox-LDL) to CD36-transfected cells and the mechanisms by which immobilized TSP1 mediated attachment and haptotaxis (cell migration towards a substratum-bound ligand) of these transfected cells. CD36 cDNA transfection of NIH 3T3 cells clearly induced a dramatic increase in binding of both soluble [125I]-TSP1 and [125I]-ox-LDL to the surface of CD36-transfected cells, indicating that there was a gain of function with CD36 transfection in NIH 3T3 cells. Despite this gain of function, mock- and CD36-transfected NIH 3T3 cells attached and migrated to a similar extent on immobilized TSP1. An anti-TSP1 oligoclonal antibody inhibited CD36-transfected cell attachment to TSP1 while function blocking anti-CD36 antibodies, alone or in combination with heparin, did not. A series of fusion proteins encompassing cell-recognition domains of TSP1 was then used to delineate mechanisms by which NIH 3T3 cells adhere to TSP1. Although CD36 binds soluble TSP1 through a CSVTCG sequence located within type 1 repeats, 18,19CD36-transfected NIH 3T3 cells did not attach to immobilized type 1 repeats while they did adhere to the N-terminal, type 3 repeats (in an RGD-dependent manner) and the C-terminal domain of TSP1. Conversely, Bowes melanoma cells attached to type 1 repeats and the N- and C-terminal domains of TSP1. However, CD36cDNA transfection of Bowes cells did not increase cell attachment to type 1 repeats compared to that observed with mock-transfected Bowes cells. Moreover, a function blocking anti-CSVTCG peptide antibody did not inhibit the attachment of mock- and CD36-transfected Bowes cells to type 1 repeats. It is suggested that CD36/TSP1 interaction does not occur upon cell-matrix adhesion and haptotaxis because TSP1 undergoes conformational changes that do not allow the exposure of the CD36 binding site.